1. Field of the Invention
This invention relates to remote control systems for operating an electrical apparatus utilizing transmission of binary coded digital information.
2. Description of the Prior Art
Operation of various electrical apparatus, such as television sets, by a remote control system consisting of a transmitter and a receiver is known in the art. In such systems a command is automatically transmitted by the transmitter in uniform intervals for such a length of time as the operating condition in the transmitter enabling the transmission of the command is maintained, such as continued depression of a push button or key.
There are instances in the use of such systems in which the receiver must recognize whether the operating condition at the transmitter has been interrupted through a brief change in the position of the associated individual switch at the transmitter. It is important for the receiver to recognize whether, during the transmission of a sequence of identical commands, the key at the transmitter has been depressed once for a long period of time or several times briefly. Examples of such situations are when the first depression of the key associated with an alternating command signifies, for example, the switching on of a specific function of the receiver, and the immediately following depression of the key signifies the switching off of the function. A second such situation is the transmission of decimals together with a command, such as for the selection of television channels. A one-time depression of the key may signify the transmission of, for example, the number 3, while a double actuation separated by a brief interval may signify the transmission of the number 33.
To accommodate such situations as above, receivers in the known remote control systems monitor the time between the successive digital signals in the receiver and the corresponding output of the receiver is determined by the respective duration of the signal free time period following the appearance of the last digital signal received. When a designated length of signal free time has been exceeded, the receiver will produce a different operational command to the electrical apparatus than when the digital signal characterizing the transmitted command appears prior to the expiration of this time period. Thus, when the time period has been exceeded, it is assumed by the receiver in the known control systems that the push button has in the interim been released.
Receivers of the type utilized in known remote control systems thus require a switching circuit for the purpose of monitoring and measuring a relatively long time period. Such circuitry requires a considerably increased circuit-cost and, moreover, an increased test time outlay. Additionally, because transmission interferences must be expected, the received pauses need not always be identical with the transmitted pause.